This invention relates to methods of forming meltblown webs and in particular to methods of forming meltblown webs containing meltblown fibers and particulate
It has been desired to provide a method of forming particle-containing meltblown webs for a variety of purposes, wherein a predetermined amount of particles is held in the web while minimizing the amount of xe2x80x9cdustingxe2x80x9d (i.e., particles undesirably dropping out of the web) the web may suffer.
Various approaches to retaining particles within a web have been proposed. One such approach discloses a self-supporting durable flexible conformable low-pressure-drop porous sheet product that contains a uniform three-dimensional arrangement of discrete particles. The sheet product includes, in addition to the particles, a web of meltblown fibers in which the particles are uniformly dispersed. The particles are physically held, such as by mechanical entanglement, in the web even though there is only point contact between the meltblown fibers and the particles. (xe2x80x9cPoint contactxe2x80x9d occurs when preformed bodies abut one another. It is distinguished from xe2x80x9carea contact,xe2x80x9d such as results when a liquid material is deposited against a substrate, flows over the substrate, and then hardens in place.) Even though the particles are mechanically entangled within the interstices of the web, a portion of the particles still undesirably drop out of the web during handling.
Another approach discloses using adhesive polymers for forming the meltblown web. In addition to being physically entrapped in the web, the particles of this approach are also adhered to the surfaces of the meltblown fibers. Even though this may be viewed as an improvement over retaining particles within a web by point contact this approach accomplishes its objective with the use of expensive adhesive polymers.
For the foregoing reasons, there is a need for an improved method of forming meltblown webs having particles substantially uniformly and homogeneously dispersed therethrough and retained therein by more than mere point contact or mechanical entanglement, wherein dusting is substantially eliminated without the addition of expensive adhesive polymers.
The present invention is directed to an improved method of forming meltblown webs having particles substantially uniformly and homogeneously dispersed therethrough that satisfies the need to substantially eliminate dusting without the addition of expensive adhesive polymers.
One embodiment of the present invention provides for a method of forming a meltblown web having at least one layer, the method including forming a first primary stream containing meltblown fibers. A first secondary stream is formed containing staple fibers and merged with the first primary stream so that the first primary stream includes the staple fibers entangled with the meltblown fibers. Thereafter, the first primary stream including the staple fibers entangled with the meltblown fibers is directed onto a moving forming surface to form a first layer having the staple fibers entangled with the meltblown fibers. After tie first layer is formed, this embodiment of the invention provides for forming at least one particle-containing layer by forming a second primary stream having meltblown fibers. A first tertiary stream is formed containing particles and merged with the second primary stream so that the second primary stream contains particle-containing meltblown fibers. A second secondary stream is formed containing staple fibers and merged with the second primary stream so that the second primary stream includes the staple fibers entangled with the particle-containing meltblown fibers. Thereafter, the second primary stream including the staple fibers entangled with the particle-containing meltblown fibers is directed onto the first layer on the moving forming surface to form a second layer having the staple fibers entangled with the particle-containing meltblown fibers.
An alternative embodiment of the present invention provides for the formation of a meltblown web having at least one layer, the method including forming a primary stream of meltblown fibers. A tertiary stream containing particles is formed and merged with the primary stream so that the primary stream includes particle-containing meltblown fibers. Thereafter, the primary stream having particle-containing meltblown fibers is directed onto a moving forming surface to form a layer including the particle-containing meltblown fibers.
Still another embodiment of the present invention provides for forming a meltblown web having at least one layer, the method including forming a primary stream containing meltblown fibers. A tertiary stream containing particles is formed and merged with the primary stream so that the primary stream includes particle-containing meltblown fibers. A secondary stream having staple fibers is formed and merged with the primary stream so that the primary stream includes staple fibers entangled with the particle-containing meltblown fibers. Thereafter, the primary stream having the staple fibers entangled with the particle-containing meltblown fibers is directed onto a moving forming surface to form a layer having the staple fibers entangled with the particle-containing meltblown fibers,